1. Field of the Invention
An object of the present invention is an improved device for the combination of two alternating signals of the same frequency. More particularly, an object of the invention is the addition of two signals of different phase and amplitude. In a special application, the invention has microwave-related uses.
In one example, the cavity resonators of a linear accelerator are supplied with a microwave signal. The electron beam produced by the cathode of this accelerator picks up the microwave energy from the cavities, becomes organized and strikes an anode target with an energy depending essentially on the energy of the picked up microwave signal. The efficiency of this picking up process is not total. In the application referred to, the microwave signal which is not absorbed by the electron beam can then be recovered and reinjected, and gets added to the supply signal. With the device of the invention, this addition is improved.
2. Description of the Prior Art
There is a known device, according to the French patent No. 86 00323, filed on behalf of the same Applicant on 10th Jan. 1986, for combining alternating signals of the same frequency wherein the problem of differences in amplitudes of signals to be added has been resolved. When a high frequency power signal is injected into a cavity resonator, the output impedance of the generator is matched with the input impedance of the cavity in such a way that there is no reflection of power. The high-frequency powers is then used to the maximum. If a beam of particles is injected into this cavity, this beam absorbs power and destroys the matching. To retrieve the situation, the cavity must be re-adapted to the source by changing the coupling coefficient. By acting in this way, the beam load is compensated for. Now, if we consider, more particularly, sections of travelling-wave linear accelerators, the power is propagated along the section, creating therein electromagnetic fields which are used to accelerate the charged particles. A portion of the power is lost in the section, in the form of losses by Joule effect in the metallic walls and in the form of energy discharged by the beam of particles. At the end of the section, there remains a part of the power which must be dissipated in an adapted load if it is sought to avoid reflecting it at the input where it would disturb the high-frequency source. In the previous patent application, it was known to reinject this part of the power in taking into account a beam load stabilized at a given value.
An improvement of the system thus consists in re-using An improvement of the this power, which is otherwise unnecessarily lost, by re-introducing it at the input of the accelerator by a system of re-circulation. A re-circulation system of this type consists essentially of a phase shifter and a coupler. For a given beam, the coupling coefficient of the coupler can be computed so that signals coming, firstly, from the source and, secondly, from the output of the accelerator, are totally confined to the load, provided that the phase shifter is appropriately set. Then, all the power coming from the source is completely used in the accelerator, apart from loss in the re-circulation circuits and in the coupler. This balance is unfortunately broken for another current value, and cannot be re-established regardless of the setting of the phase shifter. This disadvantage can be avoided by using a compensation system, especially the system described in the above-mentioned patent application. In this system, for each attenuation rate of the accelerator, namely for each value of the particle beam current, it is possible to set two phase shifters so as to cancel the signal coming out of a combination element. In this way, all the power coming from a source is completely re-used in the accelerator, with the exception of power lost in the re-circulation circuit. While this approach has been verified, it is difficult to adjust because it is difficult to automate the setting of the phase shifters. Consequently, the beam load varies, the reinjection is immediately disturbed and the efficiency of the accelerator drops considerably.
An object of the present invention is to remove these drawbacks by noting that the setting of each phase shifter is not independent but that, on the contrary, these settings are related to the function to be fulfilled. Thus, in the invention, the two phase shifters are coupled to each other according to a coupling relationship that depends on the mode of combination of the signals which it is sought to obtain; subsequently only one of the phase shifters is set, the second one following automatically according to the coupling mode, so that the matching is made automatic.